1. Field of the Invention
The invention involves processing auxiliary information, such as closed caption character information, in video signal processing systems and, more particularly, to a system for preventing and/or correcting distortion of the rendering of one character that results from an attribute or format, such as italics, of another character.
2. Description of the Prior Art
User interface (UI) systems based on Microsoft Windows 32 bit platform architecture (Win32), e.g., Microsoft Windows Compact Edition (WinCE) operating system for handheld devices, implement a font system and text drawing routines that are designed to print out strings of characters. Examples of systems requiring this type of character generation capability are video signal processing systems that include auxiliary information processing capability, e.g., teletext systems and/or closed captioning systems such as those processing auxiliary information in accordance with the EIA-608 and/or EIA-708 standards. The EIA-608 standard is the broadcast video format used in television sets built in accordance with standards set by National Television Standards Committee (NTSC), which defines a video screen having a 4:3 aspect ratio. The EIA-708 standard is the standard for digital television (DTV) captioning. DTV offers a dramatically higher-quality picture, and provides a display in a wider 16:9 aspect ratio format, e.g., as seen in a movie theater. EIA stands for Electronic Industries Alliance—a trade organization alliance of the US electronics industry.
Closed captioning that complies with the above referenced standards provides characters for display that appear to be superimposed, or on top of, a video image. The characters provide textual content corresponding to the audio portion of a video program, e.g., to aid hearing impaired users. For analog television signals, such as NTSC, the standard television signal in the United States, the strings of text data are present in the vertical blanking intervals. That data is extracted and converted to character data for display on a screen at the same time as the video data is being processed. In digital television signals, the captioning data may be included as a particular group or stream of digital data packets.
Regardless of the signal type or data-delivery means, the closed caption data is used to produce close captioning characters having a foreground and a background color. In addition to the color characteristics, the characters can be stylized or have attributes or a particular format, such as being italicized. Italics is a particular way of formatting characters, for example, tilting the character to the right. The captioning characters are received one at a time for display one at a time using the graphics display capability of the operating system, e.g., Windows text drawing routines. Close captioning systems process characters one at a time to provide increased performance as no assembly of strings of characters is required. Consecutive characters are displayed one at a time on a display.
When the above described systems generate an italicized or tilted character for display, adding the italicized attribute or format to a normal character can cause the italicized character to shift or increase in width and occupy more display area than allotted for display of one character. That is, when italicized, a character can extend into and overlap the space or cell allotted for the adjacent character. Thus, an attribute or format of one character can interfere with the rendering of another character, e.g., adjacent character, and distort or corrupt the rendering of the other character. For example, since the characters are drawn or rendered one at a time, drawing the next character with the appropriate background color can cause at least a portion of the character in the previous character cell or space to be cut-off or clipped. As a result, the character display may appear distorted.